Danshi yana nuna adadin tururin ruwa a cikin iska. Idan aka yi ruwan sama, yanayi yana da danshi sosai saboda akwai tururin ruwa mai yawa a cikin iska. Akasin haka, idan tururin ruwa a cikin iska bai yi yawa ba, iskar tana bushewa. Adadin tururin ruwa a cikin iska yana bayyana ne ta hanyar danshin da ke tsakanin su.
Danshin da ke tsakanin tururi da tururin da ke cikin tururin a wani zafin jiki (tururi tururin ruwa ne). Danshin da ke tsakanin tururin da ke cikin tururin yana bayyana a cikin kashi, wanda aka tsara shi ta hanyar lissafi:
Akwai wata sabuwar kalma, wato matsin lamba na ɓangare. Matsi na ɓangare shine matsin lamba da kowace iskar gas a cikin iska ke bayarwa. Iskar ta ƙunshi nau'ikan iska daban-daban. Akwai nitrogen (78%), oxygen (21%), argon (0.90%), carbon dioxide, tururin ruwa da sauransu. Adadin matsin lamba na ɓangare daga kowace iskar gas a cikin iska ana kiransa jimlar matsin lamba (jimlar matsin lamba = matsin lamba na yanayi = matsin lamba na iska). Idan babu tururin ruwa a cikin iska, to matsin lamba na ɓangaren tururin ruwa = 0. Akasin haka, matsin lamba na ɓangaren tururin ruwa shine mafi girma idan matsin lamba na ɓangaren tururin ruwa = matsin lamba na tururin ya cika da ruwa. Matsi mai cike da tururin ruwa ya dogara da zafin jiki.
Idan matsin lamba na tururi ya kai kashi ɗaya bisa uku (danshin da ya kai kashi ɗaya bisa uku ....
